The planning for the Fourth War came after Federated SunsFirst PrinceHanse Davion signed the Federated Commonwealth Alliance document with the Lyran CommonwealthArchon, Katrina Steiner, in 3022. Secretly included in the document was a provision that called for the marriage of Hanse and Archon-Designate Melissa Steiner, which would (eventually) result in the union of those two realms in the person of Hanse and Melissa's eldest child. In order to join their realms together, they needed to create a common border. This could only be done through the conquest of intervening planets.

Hanse began by staging military exercises close to the Capellan Confederation border on a yearly basis starting in 3026. The so-called "Galahad tournaments" not only gave his troops exercise, but it got the Capellans used to large troop movements near their border.

Hanse had also instituted an elaborate spy game. The son of Quintus Allard, the director of the Federated Suns civilian spy agency (the Ministry of Information, Intelligence, and Operations or MIIO for short), Justin Allard, was publicly ridiculed and exiled. After Justin Allard publicly embraced his Capellan heritage, started calling himself Justin Xiang (his mother's maiden name), and won the Solaris VII championship, Chancellor Liao welcomed him into his intelligence agency. Unbeknownst to all but Justin, Hanse, and Quintus, Justin Xiang Allard was actually a double agent working for his father. In addition, another deep cover agent, Alex Mallory, had also infiltrated the Maskirovka (the Capellan spy agency). By the time the war started, these two men were the #2 and #3 men in the Maskirovka.

Hanse was also aware of a traitor in his midst. His half-stepbrother, Duke Michael Hasek-Davion, nursed a bitter grudge against Hanse because he wanted to be Prince (for a more detailed analysis, see this article) and had been covertly passing information to Maximillian Liao. Hanse was able to use Duke Michael to feed false troop information to the Capellans, who were left woefully out of position for the assault.

Prince Davion had also signed an independent truce with Candace Liao, heir to the Chancellorship and Duchess of the St. Ives Commonality (roughly one-fifth of the Capellan Confederation).

On the Lyran side, Archon Katrina was at first extremely reluctant about a joint offensive with the Federated Suns. However, intelligence reports indicated growing increased public unrest in the Rasalhague military district. Since the district's governor, Mies Kurita, exaggerated the insurrection for several years to get his way, even the frightening increase of hostilities against the Draconis Combine was ignored by the Combine's government and even by DCMS commanders within the district.

The LIC made good use of the situation by supporting the Rasalhaguian resistance, the so-called Tyr Resistance Movement. The conquered people of Rasalhague had maintained an organized resistance for centuries, even though the majority of it had been stopped by the mid-24th century. The Lyrans used this resistance in exchange for the promise of freedom. In addition, LIC-analysts believed, that the DCMS-units along the border made a critical error: they felt into garrison routines. Retirees, recruits and supplies were provided according to a rigorous timetable, resulting in a very seasonal strength of individual units along the border with the Lyran Commonwealth.[1]

In response to the F-C alliance, the leaders of the other three Successor States, the Capellan Confederation, Free Worlds League, and Draconis Combine came together under a loose alliance known as the Kapteyn Accords. This alliance, which was overseen by ComStar, lacked the uniting features of the FedCom alliance. Indeed, negotiations were almost derailed when Janos Marik and Maximilian Liao were informed that the other party would be involved. The Accords were signed, but did not overcome long years of distrust.

Perhaps the most important social event until that time occurred on Terra. On 20 August 3028, six months after her eighteenth birthday, Hanse Davion married Melissa Steiner. The leader of every Successor State was there, including their aides, heirs, and other VIPs. At the wedding reception, Hanse Davion uttered one of the most quoted lines in Inner Sphere history, "My dear... I give you the Capellan Confederation." To the leaders of the Inner Sphere, it seemed like this touched off the 4th War, but, in fact, troops had already invaded the day before.

The AFFS exploited a strategic weakness in CCAF structure. The Capellans lightly garrisoned border worlds and relied on a strategic reserve to intervene quickly to achieve local superiority. The Capellan Confederation Armed Forces were outnumbered by nearly four to one by the AFFS, however. Their strategy was well-suited to dealing with the constant raiding of the Third Succession War, but left the Capellans unable to respond when multiple planets were hit at the same time as Hanse Davion brought the entirety of his army to bear. Coupled with overwhelming force and an infiltrated command structure, the Capellans were overrun.

The truce that Hanse Davion had struck with Candace Liao paid off. Amid a romance with Candace, Justin Xiang Allard outed himself as a FedSuns agent to her and returned to FedSuns space with her. She brought the St. Ives Commonality with her and formed her own independent nation, the St. Ives Compact. This decision left her younger sister Romano as the heir-apparent to the Celestial Throne.

ComStar also took an interest in the course of the war. The supposedly neutral power desired smaller, more fragmented nations that would be easier to manipulate, but the 4th War seemed to promise a mighty Federated Commonwealth. ComStar decided to slow the AFFS' progress by imposing a communications interdiction. They faked an AFFS attack on the HPG on Sarna and used the "incident" as the excuse they needed. Unbeknownst to ComStar, Hanse Davion had changed the units he used to assault Sarna at the last minute, alerting him to ComStar's duplicity. Despite that, Hanse could not afford to openly challenge ComStar, so he made no public statement about it. The interdiction effectively stopped all interplanetary communication within the Federated Suns, as well as any communication in or out. Hanse still had another trick up his sleeve. The New Avalon Institute of Science had recently duplicated the ability to send communications between worlds with their fax machines, but they were much slower than what ComStar could manage. These so-called "black boxes" were pressed into service, but Hanse found it increasingly difficult to coordinate his military.

ComStar showed their perfidy once more towards the end of the war. In order to set back the technological progress of the Successor States, ComStar executed a raid on the New Avalon Institute of Science. They disguised themselves as the Death Commandos, the elite commandos of the Capellan Confederation and personal bodyguards of ChancellorLiao. During the battle, Prince Hanse Davion took to the field himself in his BattleMaster. The attack did only superficial damage to the university, but did great damage to ComStar in Hanse Davion's eyes. His spies in the Capellan Confederation later reported to him that the Death Commandos were on the planet Kathil during the time of the raid, so there was no way they could have pulled it off. Coupled with the knowledge of the supposed HPG destruction on Sarna, Hanse came to the only logical conclusion.

In order to find the forces for his massive assault on the Capellan Confederation, Hanse Davion had to strip away large quantities of troops from the border with the Draconis Combine. Far from leaving himself open to attack, Hanse contracted the mercenary unitWolf's Dragoons to defend his border. Jaime Wolf, the commander of the Dragoons, and CoordinatorTakashi Kurita held a deep personal dislike of each other, so Jaime was able to goad Coordinator Kurita into throwing everything he could spare at his Dragoons.

By the end of the war, Wolf's Dragoons had been reduced from over five regiments to one reinforced regiment. In gratitude, Hanse Davion granted Jaime Wolf and his Dragoons the conquered planet of Outreach in perpetuity.

The Lyrans had many things going for them. In the Rasalhague Military District rebels were fomenting insurrection, but since the districts governor overrated the public unrest for several years to get his will, no one believed his cries for alarm anymore. The Lyrans also profited from Takashi Kurita's obsession with Wolf's Dragoons. Furthermore, the lightning offensive also shocked the defending DCMS forces as well as the Kurita high command. However, the LCAF still faced a much better organized and equipped enemy than the AFFS. In addition, the LCAF also had to worry about the Free Worlds League.

The Lyran offensive had different goals than Operation Rat. Instead of capturing enemy territory, the primary goal of Operation Gotterdammerung was to engage as many DCMS regiments as possible and to prevent them from being used against the Federated Suns. Thus, the offensive would be considered a success if the LCAF could capture a total of 10 worlds, and deal out more damage to the defending DCMS forces than it received. Consequently, Operation Gotterdammerung was designed quite differently from the AFFS' Operation Rat. Whereas the AFFS executed several different "waves", effectively leapfrogging each other, the Lyrans pushed into the Draconis Combine on a very broad front. When Kurita forces retreated, LCAF units along the front were ordered to pursue their counterparts to damage them even further. This forced the LCAF to spread thin and left only few reserves against any counterattacks by the DCMS, however. In addition, it gave Lyran troops little time to rest and refit.[3]
The Lyran offensive against the Draconis Combine was stalled basically due to internal machinations by Aldo Lestrade and his Free Skye Movement. Lestrade let Theodore Kurita know, that he was willing to loose a few worlds to get a reason to separate the Isle of Skye from the rest of the Commonwealth. Subsequently, he stripped parts of the Isle of Skye from troops. However, Theodore Kurita wasn`t content with a few worlds but the whole Isle of Skye. When the Combine struck, the DCMS captured a couple of worlds that put them within one jump of Skye, the capital of the Isle of Skye.[4]
Though counterattacks by the 10th Lyran Guards supported by Loki-operatives and later the 1st Royal Guards and Barret's Fusiliers stopped the Kurita offensive in their tracks, the counterattack clearly pointed out the fragile situation of the exhausted Commonwealth troops.[5] When the DCMS took a more defensive stance in 3030, the Archon gladly ordered the LCAF to do the same.[6]

However, the offensive was a stunning success. Ultimatively, the LCAF captured a total of 53 Combine worlds from the Dieron and Rasalhaague Military Districts in addition to another 8 worlds from the Free Worlds League.[7]

LCAF forces on the Free Worlds League's border were even weaker. When the FWLM attacked during Operation Dagger, the Lyran forces were redeployed not to prevent the Marik forces from taking Lyran planets, but to make them pay more dearly. On Wyatt for example, the approaching Marik regiments were attacked by Commonwealth fighters waiting for them at the jump point immediately after the FWLM troops appeared. The Lyran troops damaged a couple of DropShips, causing considerable damage to the Marik troops and retreated afterwards. However, Marik forces captured several Lyran planets ultimately.[8][9]

Operation Dagger significantly bogged down upon Janos Marik receiving word that Andurien forces, claiming that they were attacked by Capellan terrorists, had begun assaults on Capellan worlds.[10] Subsequent, the Free Tikonov forces invaded Marik space and the LCAF attacked Callison, the home base of the elite Marik Guard regiment. The Marik Guard was preparing to leave the planet to defend the Free World's League against the Tikonov forces with most of its forces already on board its DropShips. Consequently, the attacking Hsien Hotheads regiment severely damaged the elite defenders and captured Callison.[11][12]
Thereupon, the LCAF bluffed the LCCC into believing them, that the LCAF was preparing for another major offensive against the Free World's League, much like Theodore Kurita's ruse during the War of 3039. Believing, that he would lose the planets near Terra anyway, but unwilling to lose his precious defending forces, the startled Captain-General Janos Marik ordered his troops to abandon several worlds as well as all the Lyran worlds captured by the FWLM during Operation Dagger.[13]

Janos Marik was quite satisfied watching the other successor states to "let the fools knock themselves dizzy while we sit back, rest, and enjoy". However, his allies convinced him to attack the Lyran Commonwealth's weakly defended border to the Free Worlds League.[14] Consequently, Operation Dagger was born. Operation Dagger was not intended to be a major offensive, though. [15] Instead, Marik forces carried out a number of raids and heavy probes to find and exploit weak spots in the Commonwealth's defence. Consequently, the 25th Marik Militia and the 1st Regulan Hussars attacked Wyatt, Smithson's Chinese BanditsMilton and the 30th Marik Militia invaded Phecda. The primary goal was the isolation and the destruction of two key Commonwealth units on Wyatt, the 11th Lyran Guards and the 17th Arcturan Guards. Unfortunately for the Marik troops, the LCAF forces had been tipped off about the attack and Commonwealth fighters engaged the Marik jumpships just when they materialized, inflicting severe damage on the 25th Marik Militia. Subsequent, the Commonwealth units retreated. On the other planets, the Marik units were often surprised by either the complete absence of defending units or unexpected heavy resistance. However, since many of the defending Commonwealth troops had been redeployed, the FWLM captured a couple of planets, including Wyatt and Poulsbo.[16]
Thus, the LCCC considered Operation Dagger a success, despite the FWLM troops failed to pin down and destroy the 11th Lyran Guards and the 17th Arcturan Guards as well as the losses of the 25th Marik Militia on Wyatt. However, Operation Dagger bogged down, when Andurien forces seized the Capellan worlds of Palladaine and invaded others. Only urgent messages by Janos Marik to Sian and Andurien stopped the conflict. His hopes of staying aloof from the conflict were shattered, tough.[17]

Hitherto relatively unscathed in the conflict, the Free Worlds League was surprised to find itself the target of an invasion by the newly created Tikonov Free Republic. Five Republican 'Mech regiments supported by 44 conventional regiments invaded the worlds of Talitha, Van Diemen IV, Procyon and Wasat. On Procyon the 2nd Sirian Lancers were outnumbered two-to-one, but held out untill their commander was killed. On Wasat The 15th Marik Militia retreated from Wasat, when their commander was captured. On Talitha and Van Diemen IV only militia remained, which were quickly overwhelmed by Free Tikonov forces.[18]

The Tikonov offensive stunned the League leadership, who had been in trade negotiations with Pavel Ridzik's government right up until the attack (mostly because Pavel Ridzik failed to inform his diplomatic corps of his plans). The Lyran leadership took advantage of the lull and launched an assault on Callison with Lyran officers commanding the mercenary Hsien Hotheads. Catching half of the Marik Guard in their transports, the Hotheads dealt the unit a number of startling defeats and reversals. Eventually the Lyran commander offered to let the Marik Guard retreat in exchange for Callison and spare parts, which the Guard, unable to resist, accepted.[19]

At the same time, the LCAF started massive communication traffic and JumpShip movement that led the LCCC into believing a new Commonwealth offensive against the Free Worlds League was about to begin. Janos Marik, with trouble on all fronts, ordered a strategic withdrawal from eight worlds: Marcus, Zosma, Denebola, Castor, Devil's Rock, Oliver, Alula Australis, and Graham IV. FWLM forces also retreated from Milton, Phecda, Wyatt, Poulsbo, Timbiqui and Launam which they had captured during Operation Dagger. What Janos Marik did not know, was that the Lyran movements at the time were a bluff and that Pavel Ridzik's recent death had meant an end to the Tikonov invasion.[20]

The Federated Suns conquered roughly a third of the Capellan Confederation and two commonalities seceded from the realm. The CCAF lost nearly two-thirds of their combat strength. In addition, the AFFS captured the bulk of the Capellan heavy industries, including the Earthworks factory on Tikonov. While the Tikonov Free Republic joined the Federated Suns, the St. Ives Compact continued to remain politically independent, though dependent on AFFS military aid to avoid being conquered by the Capellan Confederation. The conquered worlds were incorporated into the Federated Commonwealth as the Sarna March.

Maximilian Liao went stark-raving mad. His younger daughter, Romano Liao, ran the nation until his suicide. With her military shattered, and much of her nation's industry under foreign control, Romano struggled to ensure the Capellan Confederation's survival. It would be decades before the Capellan Confederation would be a threat once more.

ComStar and the Federated Suns negotiated a settlement to restore communications to the Suns that included stationing ComGuard troops within FedSuns space to protect their HPGs from further attack. Secretly, ComStar's intelligence agency, ROM, and MIIO fought a shadow war for years.

The Draconis Combine lost 53 worlds along the Lyran border, mostly in the Rasalhaague and Dieron Military Districts and captured in return only two Lyran planets. However, the DCMS captured a few planets from the Federated Suns, but the gains were nowhere near the Combine's losses. In addition, many of its best regiment were destroyed or severely damaged by either the LCAF or Wolf's Dragoons. The only bright spot for the Combine was the rise of Theodore Kurita during the war.[23]